Wires of long length are carried on spools of all kinds. These spools enable the efficient transport and handling of the wire without the wire getting entangled or the end getting lost. Wire spools are rotating in machinery on rotatable axes supported at both ends, cantilever axes with a counter fixture, on vertical spindles or between two rotatable pintles. As the spools are many times running at high to very high speeds it is a matter of elementary safety that they should be held firmly during rotation.
When a spool runs empty (or full) their replacement with full (or empty) spools should go smoothly, safe and with little effort in order not to lose time in the production process. Sometimes spools are well adapted for their use in unwinding but may not be optimal for winding wire on. For example the bore hole of a spool may be small and sufficient for the use on an axis of a pay-off installation running at low speed and low tension. Unfortunately, the same bore hole size may not be adequate to use the same spool on a take-up unit where winding forces and winding speeds are higher.
This becomes particularly relevant when the wire is rather heavy such as in the case of metal wires like steel wires, steel filaments or steel cords. The weight of wire held by the spool is high due to the high specific weight of steel and the long lengths involved. The mass of wire held by a spool may vary between 5 kg to 500 kg while the spool itself may weigh between 0.5 to 50 kg.
Typically spools are mounted by sliding the bore hole over a cantilevered shaft mounted on a rotatable disc. A cantilever mount is many times preferred as the side opposite to the rotatable disc remains free and accessible to the operator. No counter support is needed provided the spindle has sufficient diameter to hold the load. Only a chuck is needed to secure the spool on the spindle. Usually a drive pin is mounted on the rotatable disc that engages with an off-centre drive hole in the spool. In this way torque is transferred between the driven or braked rotatable disc and the spool. The loading of an empty spool can be pretty challenging for the operator in that he must first aim to insert the shaft into the bore hole and then to engage the drive hole with the drive pin. Any improvement made to the loading or unloading of empty or full spools on a steel wire processing installation is therefore welcomed.
Various solutions have been suggested to hold spools on their shafts, in particular for cantilever mounted spools. As the spools used are generally made of steel that can be attracted by a magnet it may therefore seem a plausible solution to use magnetic force to hold the spools to the installation. However, the use of magnetic forces to mount spools seems in general to be disliked:                When electromagnets are used a constant supply of current is needed towards a turning disc implying a rotative electrical contact. The rotative contact is prone to wear. Upon an electricity failure, the spools are no longer held and can come lose from the spindle. Also electromagnets do consume a lot of energy when active.        Permanent magnets—as described in U.S. Pat. No. 3,396,919—can only be used for spools with low masses as the spools have to be pulled off from the rotatable disc thereby overcoming the magnetic attractive force. For heavy and full spools such force is difficult to overcome manually.        
The inventors have therefore come up with the following solution.